Compacted/vermicular graphite cast iron for orbital or fixed scroll and manufacturing method of orbital or fixed scroll using the same

ABSTRACT

Compacted/vermicular (CV) graphite cast iron for an orbital or fixed scroll and a method for manufacturing an orbiting or fixed scroll using the same are provided. The CV graphite cast iron may includes C: 3.4˜3.9%, Si: 1.7˜2.6%, Mn: 0.2˜0.8%, P: 0.02˜0.07%, S: 0.01˜0.03%, Ti: 0.02˜0.1% by weight ratio, with the remainder including iron (Fe) and other impurities. A CV ratio may be 50% or more.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority under 35 U.S.C. §119 to Korean Application No. 10-2013-0025256, filed in Korea on Mar. 8, 2013, whose entire disclosure is hereby incorporated by reference.

BACKGROUND

1. Field

This relates to a compacted/vermicular (CV) graphite cast iron for an orbital or fixed scroll and a manufacturing method of an orbital or fixed scroll using the same.

2. Background

A scroll compressor may compress a refrigerant gas by changing a volume of a compression chamber formed by a fixed scroll and an orbiting scroll disposed to make an orbiting movement with respect to the fixed scroll. Compared to a reciprocating compressor or a rotary compressor, a scroll compressor may have relatively high efficiency, may generate relatively low vibration and noise, and may be smaller and lighter.

The orbiting and fixed scrolls may include a disk plate and a wrap. The wrap may extend in a spiral form with respect to the disk plate, whereby the wrap and the disk plate are engaged to form a compression chamber. In a scroll compressor, various factors may affect operation efficiency, such as, for example, a ratio (Hm between a height and a thickness of the wrap. Within a limited range, as the wrap is thicker and higher, compression efficiency of the compressor is increased. However, since the overall volume of a compressor may be determined in advance, the ability to increase the height of the wrap may be somewhat limited. A reduction in the thickness of the wrap may be limited by strength of a material of the wrap. Further, such orbiting or fixed scrolls may be manufactured by a casting method using gray cast iron, which is subject to limitations in reducing a thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein:

FIG. 1 illustrates an exemplary fixed scroll and an exemplary orbiting scroll.

FIG. 2 is a photograph of an internal structure of compacted/vermicular (CV) graphite cast iron, according to an exemplary embodiment as broadly described herein.

FIG. 3 is a photograph of an internal structure of compacted/vermicular (CV) graphite cast iron, according to another exemplary embodiment as broadly described herein.

DETAILED DESCRIPTION

Description will now be given in detail of exemplary embodiments, with reference to the accompanying drawings. For the sake of brief description with reference to the drawings, the same or equivalent components will be provided with the same reference numbers, and description thereof will not be repeated.

As mentioned above, CV graphite cast iron may be used as a material of an orbiting scroll 30 and/or a fixed scroll 40, and an appropriate range of each component may be based on performance required for a scroll compressor. Hereinafter each component will be described, and unless otherwise mentioned, each content is expressed by a weight ratio.

Carbon (C): 3.4˜3.9%

In CV graphite cast iron, according to an exemplary embodiment, the content of carbon (C) may be, for example, 3.4˜3.9%. In certain embodiments, the content of carbon (C) may be 3.5˜3.9%. In certain embodiments, the content of carbon (C) may be 3.6˜3.9%. In certain embodiments, the content of carbon (C) may be 3.4˜3.5%.

In cast iron, carbon (C) may exist as graphite or in the form of carbide represented by Fe3C. Thus, in a case in which the content of carbon is small, since most carbon exists in the form of carbide, a spheroidal graphite structure rarely appears, so the content carbon (C) is added by an amount greater than or equal to 3.4% to obtain a uniform flake graphite structure. As the content of carbon (C) increases, a freezing point is lowered, improving castability, but a deposition amount of graphite may increase brittleness and negatively affect tensile strength. Namely, the highest tensile strength may be obtained when carbon saturation (Sc) ranges approximately from 0.8 to 0.9, and thus, a maximum limitation of the content of carbon may be set to 3.9% to obtain good tensile strength.

Silicon (Si): 1.7˜2.6%

In CV graphite cast iron, according to an exemplary embodiment, the content of silicon (Si) may be, for example, 1.7˜2.6%. In certain embodiments, the content of silicon (Si) may be 1.8˜2.6%. In certain embodiments, the content of silicon (Si) may be 2.1˜2.6%. In certain embodiments, the content of silicon (Si) may be 2.1-2.6%.

Silicon (Si), a graphitizer, may decompose a carbide to precipitate graphite. Namely, addition of silicon (Si) may increase an amount of carbon. In addition, silicon (Si) may allow a micro-graphite structure existing in cast iron to grow as a flake graphite structure. The grown flake graphite structure is generated as spheroidal graphite by magnesium, a nodularizer, or the like. In particular, mechanical performance of a bainite matrix structure is increased according to an increase in the content of silicon. Namely, addition of a large amount of silicon (Si) may strengthen the bainite matrix structure to enhance tensile strength, and this is more conspicuous when the content of silicon is 3.0% or less. This is because, as the content of silicon is increased, a diameter of graphite is reduced and an amount of ferrite is increased to accelerate bainite transformation.

Namely, when Si/C is increased, an amount of graphite is reduced and tensile strength may be enhanced as the matrix structure is strengthen due to high silicon. This may be remarkable when inoculation is performed on a molten metal.

However, if the content of silicon exceeds 2.6%, such an effect may be saturated. In addition, if the content of silicon is too high, the content of carbide is reduced to lower hardness and abrasion resistance, make it difficult for a material to be melted, and transform an austenite structure into a martensite structure during a follow-up cooling process to result in an increase in brittleness. In addition, as the content of silicon is increased, heat conductivity is lowered to make a temperature distribution non-uniform during cooling or heating to increase residual stress. Thus, the content of silicon is determined as 1.7˜2.6%.

Manganese (Mn): 0.2˜0.8%

In CV graphite cast iron, according to an exemplary embodiment, the content of manganese (Mn) may be, for example, 0.2˜0.8%. In certain embodiments, the content of manganese (Mn) may be 0.2˜0.52%. In certain embodiments, the content of manganese (Mn) may be 0.52˜0.8%.

Manganese (Mn), a white cast iron acceleration element hampering graphitizing of carbon, may stabilize combined carbon (namely, cementite). Manganese (Mn) may also hinder precipitation of ferrite and refine pearlite, so it may be advantageous to make a matrix structure of cast iron pearlite. In particular, manganese (Mn) may be combined with sulfur of cast iron to create manganese sulfide. Manganese sulfide may float to a surface of a molten metal so as to be removed as slag, or may remain in cast iron as a non-metallic inclusion to prevent generation of iron sulfide. Namely, manganese (Mn) may neutralize harm of sulfur. In order to accelerate pearlite and remove a sulfur component, manganese (Mn) may be contained in an amount of, for example, 0.2˜0.8%.

Phosphor (P): 0.02˜0.07%

In CV graphite cast iron, according to an exemplary embodiment, the content of phosphor (P) may be, for example, 0.02˜0.07%. In certain embodiments, the content of phosphor (P) may be 0.02˜0.06%. In certain embodiments, the content of phosphor (P) may be 0.06˜0.07%.

Phosphor (P) forms a compound of iron phosphide (Fe3P) and exists as a ternary eutectic steadite together with an iron carbide. The iron phosphide may be easily undercooled and easily cause segregation in casting. Thus, as the content of phosphor (P) is increased, brittleness is increased and tensile strength is rapidly degraded. Thus, the content of phosphor (P) may be 0.02˜0.07%.

Sulfur (S): 0.01˜0.03%

In CV graphite cast iron, according to an exemplary embodiment, the content of sulfur (S) may be, for example, 0.01˜0.03%. In certain embodiments, the content of sulfur (S) may be 0.012˜0.02%. In certain embodiments, the content of sulfur (S) may be 0.013˜0.019%.

Addition of a relatively large amount of sulfur (S) may degrade fluidity of a molten metal, may increase shrinkage, and may cause a shrinkage cavity or cracks. Thus, sulfur (S) may be contained in as small an amount as possible. In this case, when sulfur (S) is contained within the range of 0.01˜0.03%, a detrimental influence may not be so great, so sulfur (S) may be managed to be within the content.

Titanium (Ti): 0.02˜0.1%

In CV graphite cast iron, according to an exemplary embodiment, the content of titanium (Ti) may be, for example, 0.02˜0.1%. In certain embodiments, the content of titanium (Ti) may be 0.02˜0.06%. In certain embodiments, the content of titanium (Ti) may be 0.06˜0.1%.

Titanium (Ti) may subdivide graphite, accelerate formation of pearlite, and increase high temperature stability of pearlite. Also, titanium (Ti) may have strong deoxidation and denitrification with respect to a molten metal. Thus, when titanium is added, graphitizing may be accelerated. Since titanium reduces a size of graphite, tensile strength may be increased, chilling may be prevented, and abrasion resistance may be improved. To this end, titanium may be contained in an amount of, for example, 0.02˜0.1%.

By mixing the elements having aforementioned characteristics, CV graphite cast iron, according to embodiments as broadly described herein, may be produced and may be used to manufacture an orbiting or fixed scroll of a scroll compressor. Hereinafter, a manufacturing method thereof will be described.

(1) Smelting

The foregoing elements may be selected in appropriate ratios to prepare a raw material, and the raw material may be put into a middle frequency induction furnace and heated to be melted, and subsequently smelted. The smelted first molten metal may be taken out of the furnace using a ladle at a temperature ranging from approximately 1500° C. to 1540° C.

(2) Spheroidization and Inoculation

A nodularizer for nodularizing graphite and an inoculant may be inoculated to the molten metal smelted in the smelting process. In this case, magnesium (Mg), calcium (Ca), and rare earth resources (RE), known to accelerate nodularization of graphite, may be used as the nodularizer. In detail, a rare earth element silicon iron magnesium alloy (FeSiMg6RE1) having components such as Mg: 5.5˜6.5%, Si: 44-48%, Ca: 0.5˜2.5%, AL<1.5%, and RE: 0.8˜1.5% may be added in an amount of 0.5˜0.9% over the mass of the first molten metal.

Inoculation may generate a large amount of graphite nucleus to accelerate graphitizing, and may uniformly distribute graphite, and may increase strength. As an inoculant, a barium silicon iron alloy (FeSi72Ba2) may be used and the content of inoculant is 0.4˜1.0% of the mass of the first molten metal.

(3) Despheroidation

A denodularizer may be injected into the spheroidized and inoculated second molten metal to stop spheroidizing. A denodularizer may include Si, S, O, and Al as principal ingredients, and the content thereof may be, for example, 0.01˜0.02% over the mass of the second molten metal.

(4) Casting

The third molten metal including the denodularizer may be injected into a mold manufactured in advance to have a cavity having a desired shape and cooled. The denodularizer may be directly injected into the ladle, or may be injected together when the second molten metal is injected into the mold.

(5) Machining

The semi-product obtained from the casting process may be ground and machined to have final dimensions and shape.

Table 1 shows compositions and measured CV ratios of six embodiments manufactured according to a manufacturing method as embodied and broadly described herein. In the embodiments below, only the content of sulfur (S) and injection ratios of a nodularizer, and a denodularizer are differentiated, and all of them has a CV ratio of 50% or more. Here, the content of C, Si, Mn, P, and Ti of the embodiments are as shown in Table 2.

TABLE 1 Embodiments S Nodularizer Denodularizer CV ratio 1 0.012 0.58 0.011 75% 2 0.019 0.75 0.011 65% 3 0.013 0.75 0.011 55% 4 0.019 0.58 0.2 63% 5 0.019 0.58 0.011 50% 6 0.012 0.58 0.2 78% 7 0.013 0.75 0.2 85% 8 0.016 0.68 0.011 65%

TABLE 2 Component C Si Mn P Ti Content 3.4 2.2 0.52 0.06 0.06

FIGS. 2 and 3 are photographs of internal structures of two of the above embodiments, respectively, in which it can be seen that the embodiments include an appropriate range of CV graphite cast iron.

A compacted/vermicular (CV) graphite cast iron for an orbital or fixed scroll and a method of manufacturing such an orbital or fixed scroll, as embodied and broadly described herein, may be capable of further reducing a thickness of a wrap part, in place of gray cast iron.

Compacted/vermicular (CV) graphite cast iron for an orbital or fixed scroll, as embodied and broadly described herein, may include C: 3.4˜3.9%, Si: 1.7˜2.6%, Mn: 0.2˜0.8%, P: 0.02˜0.07%, S: 0.01˜0.03%, Ti: 0.02˜0.1% by weight ratio and iron (Fe) and any inevitable impurity comprising the remainder, and having a CV ratio of 50% or more.

Gray cast iron may have excellent castability, vibration attenuation, and heat conductivity, thus being appropriate for casting, but as mentioned above, the gray cast iron has low strength and toughness, and thus, has low abrasion resistance and impact resistance. Meanwhile, nodular graphite cast iron may have improved physical properties compared to those of gray cast iron. In case of nodular graphite cast iron, precipitated graphite has a spherical shape, having excellent abrasion resistance, heat resistance, and corrosion resistance, having high strength and toughness, and having good cuttability so as to be very appropriate for casting. However, nodular graphite cast iron has low heat conductivity, making it difficult to be manufactured to have a complicated form.

In a scroll compressor, a form of an orbiting or fixed scroll greatly affects compression efficiency. One of them is a ratio between a height (H) and a thickness (t) of a wrap part. Namely, as a thickness of a wrap part is smaller, gas pressure volume is increased and operation efficiency (or work efficiency). However, there is a limitation in increasing the exterior of a compressor and a height of a wrap part is limited, and thus, in order to enhance compression efficiency, a thickness needs to be reduced. However, in the conventional gray cast iron, if a thickness thereof is reduced, strength cannot be satisfied, and in case of nodular graphite cast iron, it is not easy to cast a wrap part to have a small thickness due to a problem of castability.

Compacted/vermicular (CV) graphite cast iron may refer to cast iron in which a form of graphite precipitated in a matrix structure has an intermediate form between flake graphite and spheroidal graphite, and it is also called vermicular graphite cast iron or compacted graphite cast iron. CV graphite cast iron has advantages of both gray cast iron and spheroidal graphite cast iron. Thus, the use of CV graphite cast iron as a material of an orbiting or fixed scroll may effectively reduce a thickness to enhance compression efficiency of a scroll compressor.

A CV ratio may refer to a ratio of an area of CV graphite to an area of graphite precipitated in a structure. According to research results of the inventor of the present application, it was confirmed that when a CV ratio is 50% or more, it is appropriate as a material of an orbiting or fixed scroll of a scroll compressor.

A method for manufacturing an orbiting or fixed scroll, as embodied and broadly described herein, may include mixing raw materials including C: 3.4˜3.9%, Si: 1.7˜2.6%, Mn: 0.2˜0.8%, P: 0.02˜0.07%, S: 0.01˜0.03%, Ti: 0.02˜0.1% by weight ratio and iron (Fe) comprising the remainder and smelting a first molten metal; injecting nodularizer into the first molten metal to obtain a second molten metal; injecting a denodularizer to the second molten metal with the nodularizer injected thereto to obtain a third molten metal; casing a third molten metal including the denodularizer by using a mold to obtain a semi-product; and machining the semi-product to have final dimensions and shape.

In manufacturing CV graphite cast iron, in a state in which a nodularizer is injected and spheroidizing is performed, a denodularizer is injected to hamper the progress of spheroidizing, thus precipitating CV graphite. In the related art, CV graphite cast iron is manufactured by using a wire feeding method or by injecting a vermicular agent, which, however, incurs high manufacturing costs and it is difficult to control to have an appropriate CV ratio. In contrast, in the present disclosure, CV graphite cast iron may be easily produced by using a nodularizer and denodularizer.

A rare earth element silicon magnesium alloy (FeSiMg6RE1) may be used as the nodularizer. Here, the nodularizer may be added in an amount of 0.5˜0.9% of the weight of a molten metal.

The denodularizer may be injected in the process of injecting the second molten metal into a mold.

The denodularizer may include Si, S, O, and Al as principal ingredients. The content of the denodularizer may be 0.01˜0.02% of the second molten metal.

In the process of injecting the nodularizer, a barium silicon iron alloy (FeSi72Ba2) may be injected as an inoculant, and the content of the inoculant may be injected in an amount of 0.4˜1.0% of the mass of the first molten metal.

According to one aspect, by using CV graphite cast iron having the advantages of gray cast iron and nodular graphite cast iron, as a material of an orbiting or fixed scroll, a thickness of a wrap part may be effectively reduced without degrading rigidity, thus enhancing compression efficiency of a scroll compressor. In addition, since CV graphite cast iron has low density, a weight of the compressor may also be reduced.

According to another aspect, since CV graphite cast iron may be manufactured by sequentially using a nodularizer and a denodularizer, CV graphite cast iron may be easily produced, compared to the case of using a wire feeding method or injecting a vermicular agent as in the related art.

Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art. 

What is claimed is:
 1. Compacted/vermicular (CV) graphite cast iron for at least one of an orbiting scroll or a fixed scroll, comprising C: 3.4˜3.9%, Si: 1.7˜2.6%, Mn: 0.2˜0.8%, P: 0.02˜0.07%, S: 0.01˜0.03%, Ti: 0.02˜0.1% by weight ratio and iron (Fe) comprising a remainder, the cast iron having a CV ratio greater than or equal to 50%.
 2. A method for manufacturing an orbiting scroll or a fixed scroll, the method comprising: mixing raw materials including C: 3.4˜3.9%, Si: 1.7˜2.6%, Mn: 0.2˜0.8%, P: 0.02˜0.07%, S: 0.01˜0.03%, Ti: 0.02˜0.1% by weight ratio and iron (Fe) comprising a remainder, and smelting a first molten metal; injecting a nodularizer into the first molten metal to obtain a second molten metal; injecting a denodularizer into the second molten metal including the nodularizer to obtain a third molten metal; casting the third molten metal including the denodularizer in a mold to obtain a semi-product; and machining the semi-product to final dimensions to have a final shape.
 3. The method of claim 2, wherein injecting a nodularizer into the first molten metal comprises injecting a rare earth element silicon magnesium alloy into the first molten metal.
 4. The method of claim 3, wherein injecting a rare earth element silicon magnesium alloy into the first molten metal comprises injecting FeSiMg6RE1 into the first molten metal.
 5. The method of claim 3, wherein injecting a nodularizer into the first molten metal comprises injecting the nodularizer in an amount of 0.5˜0.9% of a weight of the first molten metal.
 6. The method of claim 2, wherein injecting a denodularizer into the second molten metal comprises injecting the denodularizer while injecting the second molten metal into the mold.
 7. The method of claim 2, wherein injecting a denodularizer into the second molten metal comprises injecting the denodularizer including Si, S, O, and Al as principal ingredients.
 8. The method of claim 7, wherein injecting a denodularizer into the second molten metal comprises injecting the denodularizer such that a content of the denodularizer is 0.01˜0.02% of a mass of the second molten metal.
 9. The method of claim 2, wherein injecting a nodularizer into the first molten metal further comprises injecting a barium silicon iron alloy as an inoculant.
 10. The method of claim 9, wherein injecting a barium silicon iron alloy comprises injecting FeSi72Ba2 as an inoculant.
 11. The method of claim 9, wherein injecting a barium silicon iron alloy as an inoculant comprises injecting the inoculant in an amount of 0.4˜1.0% of a mass of the second molten metal. 